The invention relates to a low frequency transformer for an audio system and a method of making it. More particularly, the invention concerns a low frequency transformer having primary, secondary, and tertiary windings with insulation between each winding wherein one end of the tertiary winding is embedded in the insulation between the secondary winding and the tertiary winding, and the other end is grounded.
In a conventional audio system, a volume adjusting variable resistor, which is located next to a detection circuit, adjusts the volume of the sound. In order to increase the sensitivity, a high frequency transformer has been used; however, the efficiency of a high frequency transformer in the low frequency range is remarkably reduced. That is well-known fact. In order to improve the efficiency, the output voltage fluctuation of the conventional transformer is controlled by adjusting the relative distance of two magnetic iron cores lined up on a line, whose relative distance affects the amount of magnetic flux coupling the magnetic iron cores together. This type of control of the output voltage fluctuation is practically too big.
Also, in a conventional audio system, if the transformer is operating in an overloaded condition, i.e., the output of the transformer is more than the rated load of the transformer, the output signal of the transformer is distorted, in other words, audio waveshape distortion results. Furthermore, if multistage speakers are connected in parallel to the output of the transformer, a common arrangement, the output frequency of the transformer may be different than the input frequency, i.e., frequency distortion may occur.
The performance of multistage speakers connected in parallel may be improved by increasing the current in the secondary winding, i.e., by increasing the output current of the transformer. But even if this technique is used, waveshape distortion, which may occur because of a transformer overload, and/or noise, which may be caused by external interference signals or leakage current from the primary winding, could result.
In commonly known audio systems, typical impedance values for speakers, which are known as passive speakers, are 4, 8, 16, and 600 ohms. Matching the input impedance of the speakers with the output impedance of the output amplifier of the audio system is difficult. Additionally, if the output power of the amplifier does not meet the rated power of the speaker, the speaker is unusable in the higher range of its capacity.